1. Field of the Invention
The present invention relates to a system for powering a mobile device having an energy harvester which receives wireless energy and converts the energy into current. More specifically, the present invention relates to a system for powering a mobile device having an energy harvester which receives wireless energy and converts the energy into current when it is in a portal in which wireless energy is transmitted for the energy harvester of the mobile device.
2. Description of Related Art
As processor capabilities have expanded and power requirements have decreased, there has been an ongoing explosion of devices that operate completely independent of wires or power cords. These “untethered” devices range from cell phones and wireless keyboards to building sensors and active Radio Frequency Identification (RFID) tags.
Engineers and designers of these untethered devices continue to have to deal with the limitations of portable power sources, primarily using batteries as the key design parameter. While the performance of processors and portable devices has been doubling every 18-24 months driven by Moore's law, battery technology in terms of capacity has only been growing at a measly 6% per year. Even with power conscious designs and the latest in battery technology, many devices do not meet the lifetime cost and maintenance requirements for applications that require a large number of untethered devices such as logistics and building automation. Today's devices that need two-way communication require scheduled maintenance every three to 18 months to replace or recharge the device's power source (typically a battery). One-way devices that simply broadcast their status without receiving any signals, such as automated utility meter readers, have a better battery life typically requiring replacement within 10 years. For both device types, scheduled power-source maintenance is costly and can be disruptive to the entire system that a device is intended to monitor and/or control. Unscheduled maintenance trips are even more costly and disruptive. On a macro level, the relatively high cost associated with the internal battery also reduces the practical, or economically viable, number of devices that can be deployed.
The ideal solution to the power problem for untethered devices is a device or system that can collect and harness sufficient energy from the environment. The harnessed energy would then either directly power an untethered device or augment a power supply. However, this ideal solution may not always be practical to implement due to low energy in the environment, and site restrictions may limit the ability to use a dedicated energy supply. The proposed invention takes these factors into account and provides a solution for both the ideal situation and also for more restrictive circumstances.
U.S. Pat. No. 6,127,799 discloses a method and apparatus for wireless powering and recharging by use of an electromagnetic field with an antenna. The antenna may be one or more dipole antennas that are combined to form at least two subsets of dipole antenna element array, wherein one subset may be oriented at an acute or a right angle with respect to at least one other subset. The technology disclosed in U.S. Pat. No. 6,127,799 is limited by the fact that the power conversion efficiency of the antenna array is dependent on the number of dipoles. Additionally, U.S. Pat. No. 6,127,799 discloses the use of dipole antennas, which may not be practical for most battery-operated devices due to the size of the antenna and antenna array. This prior disclosure, states that the dipole antennas are used to cover more than one side of a battery that has a width of 12.5 cm which makes in impractical for certain devices and battery sizes. There are also limitations on the battery that can be used with the prior disclosure due to metal pieces inside the battery, which tend to absorb RF energy. The invention disclosed herein does not suffer from the described limitations of the antenna and battery and is applicable with any antenna and battery type.
U.S. Pat. No. 5,994,871 discloses a system for charging a secondary cell using transmitted microwave energy, however, it relies solely on the use of an existing microwave oven as the charging means.
U.S. Pat. No. 5,982,139 discloses a remote charging system for a vehicle capable of transmitting electrical energy to the electrical storage device via a wireless energy beam. The referenced patent relies on the beam being able to track the vehicle or vehicles, which limits the number of devices (vehicles) by the number of beams available at a power transmitting location. The invention disclosed herein does not suffer from this limitation and is capable of transmitting power to many devices using a single beam.
U.S. Pat. Nos. 5,411,537, 5,733,313, and 5,769,877 describe systems for providing power to implantable biomedical devices by use of electromagnetic induction techniques using power transmitting and receiving coils. The devices in these patents are limited by the fact that they can only receive power in the inductive or near-field region. Additionally, the implanted devices have a dedicated transmitter with the purpose of supplying power solely to a single implanted device.